1. Field of the Invention
The disclosure herein relates generally to the field of oil and gas production. More specifically, the present disclosure relates to a method and apparatus relates to the field of fracturing subterranean formations. Yet more specifically, the present disclosure concerns a method and apparatus of fracturing subterranean formations using a pressure producing apparatus disposable within a wellbore.
2. Description of Related Art
Stimulating the hydrocarbon production from hydrocarbon bearing subterranean formations may be accomplished by fracturing portions of the formation to boost fluid flow from the formation into a wellbore. One example of a fracturing process is illustrated in FIG. 1. In the embodiment of FIG. 1, tubing 10 is inserted into a wellbore 5 and terminates within the wellbore 5 adjacent a formation 14. Fracturing the formation, a process also known as fracing, typically involves pressurizing the wellbore to some pressure that in turn produces a fracture 18 in the formation 14. In the example of FIG. 1, a pressure source 8 is provided at surface that pressurizes fluid for delivery via the tubing 10 into the wellbore 5. A valve 12 is provided for selective pressurization of the wellbore 5. Packers 16 may be provided between the tubing 10 and the wellbore 5. Typically the inner circumference of the wellbore 5 is lined with wellbore casing 7.
The fluid being pressurized can be a completion fluid, but can also be a fracturing fluid specially developed for fracturing operations. Examples of fracturing fluids include gelled aqueous fluids that may or may not have suspended solids, such as proppants, included within the fluid. Also, acidic solutions can be introduced into the wellbore prior to, concurrent with, or after fracturing. The acidic solutions out from the inner circumference of the help create and sustain flow channels within the wellbore for increasing the flow of hydrocarbons from the formation. Packers and or plugs are sometimes used in conjunction with the pressurizing step to isolate portions of the wellbore from the pressurized fluid.
Some of the presently known systems use surface devices outside of the wellbore to dynamically pressurize the wellbore fluid. This requires some means of conveying the pressurized fluid from the pressure source to the region within the wellbore where the fluid is being delivered. Often these means include tubing, casing, or piping through which the pressurized fluid is transported. Due to the substantial distances involved in transporting this pressurized fluid, large pressure drops can be incurred within the conveying means. Furthermore, there is a significant capital cost involved in installing and using such a conveying system.
Other devices used in fracturing formations include a tool comprising propellant secured to a carrier. Disposing the device in a wellbore and igniting the propellant produces combustion gases that increase wellbore pressure to or above the pressure required to fracture the formation surrounding the wellbore. Ballistic means are also typically included with these devices for initiating combustion of the propellant.